Rework BC gem to build properly and copy its contents (no symlink)
Add jruby-openssl and bouncy-castle-java gem bits to dist src.
Minor improvements for Hash.

* Avoid creating AtomicInteger by using updater or sync.
* Avoid re-initializing "head" node.
* Avoid updating generation unnecessarily at create time.
Pull in and wire up Ruby 2.0 tests + excludes.